Area Forecast Discussion

KEY MESSAGES

- Showers and storms likely (40-70%) this afternoon and evening across portions of northeast Iowa and southwest Wisconsin. Locally heavy rainfall amounts of 2-4" will be possible where storms frequent the same locations. Additional flooding may occur where locally heavy rain falls on already saturated ground.

- Additional light rain chances (30-60%) Monday and Monday night.

- Drier and cool conditions throughout much of the upcoming week with highs generally in the 60s.

DISCUSSION

Issued at 157 PM CDT Sat Sep 19 2026

This Afternoon - Evening: Additional Heavy Rain Potential in Southwest Wisconsin and Northeast Iowa

Heavy rain impacts shift this afternoon to portions of northeast Iowa and southwest Wisconsin with additional convective development possible as shown in several of the CAMs. The general conceptual model as we head later into the day is for the front responsible for much of our rainfall to sag south with some surface convergence along it. As this occurs, some instability attempts to be advected into the region as southerly low-level flow pushes the warm sector to our south northward. The key question will be if this instability can be advected northward enough in light of the convective debris over the region to support robust convection and if the forcing will be sufficient. Many of the CAMs show some degree of convection during the afternoon/evening but disagree on how organize it would be. There are some pretty notable differences between various CAMs such as the HRRR which has shown some tendency to convect all the way up to I-90 as opposed to solutions like the ARW which keeps convection limited across the local area. Consequently, confidence remains somewhat low as to how impactful any additional storms may be but given that soils are very susceptible given several locations seeing upwards of 5-8" of rain last night.

As far as additional rainfall amounts are concerned, overall the 25th to 75th percentile spread in the recent HREF would suggest more widespread totals across portions of northeast Iowa and southwest Wisconsin of around 0.5" to 2". However, given the 90th percentile values in the HREF showing values of 2-4" would think underneath heavier storms that this could be feasible, which in turn could exacerbate any area flooding on rivers and low-lying areas. To see additional details on ongoing flooding concerns, refer to the Hydro section for more information. Otherwise, cannot completely rule out a weak tornado in far southern Grant or Clayton counties given fairly decent low-level hodograph curvature and some tendency to wetbulb the warm nose and allow for convection to be surface based. Given the lack of deep-layer shear any updrafts will be short-lived but something to consider for the mid to late afternoon timeframe.

Upcoming Week: Cool and Drier

The lower tropospheric baroclinic zone slides to the south of the region by Sunday morning, taking the bulk of the rainfall risk with it. Cannot fully rule out some stray elevated showers scraping parts of east-central Iowa during the day, but most of the region will stay dry with some sun poking out as we move through the afternoon. The mean longwave trough/cutoff low currently over the Inter- Mountain West slides eastward for Monday night into Tuesday, bringing with it the next potential for wider coverage showers. However, with the deeper moisture displaced well to the south of the region, any impacts from this rain will be low. Eastern flow off a Great Lakes/Ontario high will keep temperatures seasonably cool and mostly dry for the remainder of the week.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1247 PM CDT Sat Sep 19 2026

IFR conditions will dominate much of the forecast period as low- level moisture trapped underneath an inversion will keep cigs low throughout much of the TAF period. Showers and storms may increase in coverage later this afternoon and evening, while the bulk of the activity likely remain south of I-90, opted to include a prob30 at both KRST and KLSE to address this potential. Otherwise, IFR/LIFR cigs and vsbys likely persist until daybreak on Sunday before diurnal mixing attempts to allow some lifting of cigs to MVFR heights prior to 18z on Sunday.

HYDROLOGY

Issued at 157 PM CDT Sat Sep 19 2026

Numerous river sites continue to rise this afternoon in light of overnight rainfall. The river basins with greatest impacts remain along the Turkey, Upper Iowa, Root and Cedar River Basins where rainfall amounts of 4-8" fell. Additional rainfall this afternoon/evening may result in some additional rises, however the heaviest amounts of 2-4" will likely be localized in nature. Moderate flooding is already ongoing at the Cedar River in Lansing, MN with the crest occurring shortly. This flow will work its way downstream with additional rises expected at Austin, MN into moderate flood stage and Charles City, IA into minor flood stage this weekend and into Monday. Additional flash flooding may occur this afternoon and evening if locally heavy rainfall occurs over saturated soils as well.

ARX WATCHES / WARNINGS / ADVISORIES

WI...Flood Watch until 7 PM CDT this evening for WIZ053>055-061. MN...Flood Watch until 7 PM CDT this evening for MNZ094>096. IA...Flood Watch until 7 PM CDT this evening for IAZ008>011-018-019- 029-030.